If You can't make firmware downgrade by WIC utility - it means Your printer has newest Main board version.Epson made some changed in new main board. The solution in this case is here:Use Activation Keys and License.exe application for P600 - http://www.2manuals.com/product_info.php?cPath=107&products_id=1850

I tried to update in normal mode and after pressing 4 + 7 + Job/Status + Power
Normal Mode - that means You DONT NEED to press 4+7+Job+Power!!!!
If You press this buttons - you will put print in Program Update mode!!!
Please follow carefully our step by step guides

Download and extract this Firmware Version - FA99Z9 - http://chiplesssolutions.com/download/WF7710_FWG535TL_FA99Z9.zip
Upload firmware to printer in normal mode - dont put printer in Program Update mode.
The uploading process will stuck at 70-80% - it is ok!
Open task manager and stop updater process.
Printer will blink for about 5-15 minutes accepting firmware - then will power OFF.
Run License utility and use your ACtivation Key
Please reply about results.

Download this firmware - http://chiplesssolutions.com/download/XP240_FWF732TL_ZZ99Z9_2019.zip
Upload firmware to printer in normal mode - dont put printer in Program Update mode.
The uploading process will stuck at 70-80% - it is ok!
Open task manager and stop updater process.
Printer will blink for about 5-15 minutes - then will power OFF.
Now power on the printer - chipless firmware is installed now in your printer!
Use License and Activation Key